The present invention relates to microelectronic packaging and more particularly relates to methods of making connectors and packaged microelectronic components. In various microelectronic devices, it is desirable to provide a connection between two components, which can accommodate relative movement between the components. For example, where a semiconductor chip is mounted to a circuit board, thermal expansion and contraction of the chip and circuit board can cause the contacts on the chip to move relative to the corresponding electrically conductive features of the circuit board. This can occur during service and can also occur during manufacturing operations as, for example, during soldering operations on the circuit board.
As illustrated in certain preferred embodiments of commonly assigned U.S. Pat. No. 5,518,964 (xe2x80x9cthe ""964 patentxe2x80x9d), the disclosure of which is incorporated herein by reference, movable interconnections between elements such as a semiconductor chip and a substrate can be provided by first connecting leads between the elements and then moving the chip and the substrate away from one another through a predetermined displacement so as to bend the leads. For example, the substrate may be a connection component including a dielectric body and leads extending along a bottom surface of the dielectric body. The leads may have first or fixed ends permanently attached to the dielectric element and connected to electrically conductive features such as terminals, traces or the like on the dielectric body. The leads may also have second or releasable ends releasably attached to the dielectric body. The dielectric body, with the leads thereon, may be juxtaposed with the chip and the second ends of the leads may be bonded to contacts on the chip. Following bonding, the dielectric body and chip are moved away from one another, thereby bending the leads towards a vertically extensive disposition. During or after movement, a curable material such as a liquid composition may be introduced between the elements. The curable material is then cured such as by using heat, to form a compliant dielectric layer such as an elastomer or gel surrounding the leads. The resulting packaged semiconductor chip has terminals on the dielectric body or connection component which are electrically connected to the contacts on the chip but which can move relative to the chip so as to compensate for thermal effects. For example, the packaged chip may be mounted to a circuit board by solder-bonding the terminals to conductive features on the circuit board. Relative movement between the circuit board and the chip due to thermal effects is taken up in the moveable interconnection provided by the leads and the compliant layer.
Numerous variations of these processes and structures are disclosed in the ""964 patent. For example, the package-forming process can be conducted on a wafer scale, so that the numerous semiconductor chips in a unitary wafer are connected to connection components in one sequence of operations. The resulting packaged wafer is then severed so as to provide individual units, each including one or more of the chips and portions of the dielectric body associated therewith. Also, the leads may be formed on the chip or wafer rather than on the dielectric body. In further embodiments, also disclosed in the ""964 patent, a connector for use in making connections between two other microelectronic elements is fabricated by a generally similar process. For example, in one embodiment a dielectric body having terminals and leads as discussed above is connected to terminal structures on a temporary sheet. The temporary sheet and dielectric body are moved away from one another so as to bend the leads, and a liquid material is introduced around the leads and cured so as to form a compliant layer between the temporary sheet and the dielectric body. The temporary sheet is then removed, leaving the tip ends of the terminal structures projecting from a surface of the compliant layer. Such a component may be used, for example, by engaging it between two other components. For example, the terminal structures may be engaged with a semiconductor chip, whereas the terminals on the dielectric body may be engaged with a circuit panel or other microelectronic component.
Commonly assigned U.S. Pat. No. 6,117,694, the disclosure of which is incorporated herein by reference, teaches a microelectronic component, such as a connector or a packaged semiconductor device that is made by connecting multiple leads between a pair of elements and moving the elements away from one another so as to bend the leads toward a vertically extensive disposition. One of the elements includes a temporary support which is removed after the bending operation and after injecting and curing a dielectric material to form a dielectric layer surrounding and supporting the leads.
Despite the teachings of the ""964 patent, the ""649 patent, and the other advances in the art, there are still needs for further improvements in connection components and methods for making such connection components. Specifically, there is a need for a connection component whereby the flexible leads may be made without having to bond the lead and a method of making expandable, flexible linkages by using plating processes rather than joining processes.
One aspect of the present invention provides methods of making a component, such as a compliant connection component, having one or more leads. The leads may be flexible. One preferred method includes providing a removable or sacrificial layer having first and second surfaces and vias at spaced apart first locations of the removable layer. The vias may be formed using a broad array of processes including chemical etching processes and punching holes therein. The vias preferably extend from the first surface toward the second surface of the removable layer. The vias may be what are commonly referred to as xe2x80x9cthrough viasxe2x80x9d that extend from the first surface to the second surface of the removable layer. The vias may also be blind or partial vias that extend only part of the way between the first and second surfaces of the removable layer.
A conductive material, such as metal, may be deposited over the first surface of the removable layer and in each via to form one or more leads, each lead including a first end and a second end at a location remote from the first end of the lead. In certain embodiments, before the conductive material is deposited over the removable layer, the removable layer is placed atop the first surface of a substrate so that the first ends of the leads are connected to the substrate during the depositing a conductive material step. The conductive material deposited in the vias of the removable layer forms projections at the first ends of the leads extending downwardly into the removable layer. The projections are preferably connected with the substrate as they are formed. As a result, a separate bonding step is not required for reliably connecting the leads to the conductive metal sheet. This simplifies the process for making a connection component.
A dielectric layer may then be provided over the conductive material, such as by depositing the dielectric material over the conductive material. The removable layer may then be removed. After the removable material has been removed, the first and second ends of the flexible leads are preferably movable away from one another. For example, the second ends of the leads may be permanently attached to the dielectric layer while the first ends of the leads may be releasable and/or peelable from the dielectric layer. In preferred embodiments, a substrate, such as a conductive metal sheet including copper, is juxtaposed with the removable layer before the conductive material is deposited over the removable layer.
One preferred method of making a connection component having one or more flexible leads includes the steps of providing a removable layer having a first surface and a second surface and forming one or more vias at spaced apart first locations, the vias extending from the first surface toward the second surface of the removable layer. In certain embodiments the vias include through vias that extend from the first surface to the second surface of the removable layer. In other embodiments the vias may be blind vias that extend only partially from the first surface toward the second surface of the removable layer. The removable layer includes a soluble material. In certain preferred embodiments the removable layer includes a metal such as aluminum that may be removed, such as by using an etching solution. In other preferred embodiments the removable layer includes a soluble material such as a polymer. The removable or sacrificial layer may be removed by chemical etching, melting the removable layer, burning the removable layer or dissolving the removable layer.
After the vias have been formed at spaced apart first locations, a conductive material, such as copper, is preferably deposited over the first surface of the removable layer and in each via so as to form one or more leads atop the removable layer and to form projections in the vias extending downwardly into the removable layer. The leads formed by deposition of the conductive material preferably include first ends integrally connected with the projections at the first locations and second ends at locations remote from the first ends. In certain preferred embodiments the conductive material is deposited in the vias simultaneously with deposition of the conductive material over the first surface of the removable layer. However, in other preferred embodiments, the deposition of the conductive material over the first surface of the removable layer is not conducted simultaneously with the deposition of the conductive material in each via. For example, the conductive material may be deposited in each via from the second surface of the removable layer. The projections at the first ends of the leads and are generally hollow. In preferred embodiments, the hollow portions of the projections may be generally cup-shaped. In other preferred embodiments the projections are rivet shaped and have lower ends projecting away from the via at the second surface of the removable layer.
The conductive material may be deposited over the removable layer by methods such as electroplating the conductive material on the removable layer; electrolessly plating the conductive material on the first surface of the removable layer; chemical vapor deposition; or combinations of these methods as, for example, by first depositing a seed layer, such as chromium, over the removable layer and in the vias formed therein, and then plating or sputtering a conductive material over the seed layer.
After the conductive material has been deposited over the removable layer and in the vias to form leads, a dielectric layer is preferably provided over the conductive material. In certain embodiments, the first ends of the leads are releasable from the dielectric layer and the second ends are permanently secured to the dielectric layer. The first ends of the leads may be coated with an adhesion-reducing substance for reducing adhesion between the dielectric layer and the first ends. The leads may also be formed as set forth in commonly assigned U.S. Pat. No. 5,763,941, the disclosure of which is incorporated herein by reference, with one end of the lead permanently fastened to the dielectric layer and the other end of the lead releasably bonded to the dielectric layer, whereby the releasable end is held in place by a bond having relatively low peel strength. As a result, the first ends of the flexible leads are preferably releasably secured to the dielectric layer and the second ends of the flexible leads are permanently secured thereto.
The method of forming a compliant connection component may also include the step of forming one or more vias in the dielectric layer. The one or more vias preferably extend toward the removable layer to expose the second ends of the flexible leads. A conductive material is then preferably deposited in the vias of the dielectric layer so as to form second conductive terminals integrally connected to the second ends of the leads. The second conductive terminals are preferably electrically connected to the second ends of the leads. The second conductive terminals extend in generally vertical directions away from the removable layer. The second terminals are preferably substantially hollow and may include generally cup-shaped structures having openings that face away from the removable layer. The vias may be formed in the dielectric layer by using a laser drilling step, an etching process, other hole forming steps or a combination of the above. The vias preferably extend completely through the dielectric layer. The conductive material deposited atop the dielectric layer preferably includes a conductive metal such as copper, but may include any other material that is substantially conductive.
After the leads and the dielectric layer have been formed, the removable layer is preferably removed so that the first and second ends of the leads are movable away from one another. The removable layer preferably includes a material, such as aluminum or a polymer, that may be removed by exposure to a solvent, thereby leaving the bottom surface of the dielectric layer exposed and the leads free to bend away from the dielectric layer. In this condition, the dielectric layer supports the leads; the leads having first ends with projections integrally connected thereto projecting away from the bottom surface of the dielectric layer.
After the removable layer has been removed, the connection component may be juxtaposed with a substrate, such as a microelectronic element having contacts thereon so that the projections at the first ends of the leads may be connected with the contacts of the microelectronic element. The microelectronic element and the dielectric layer may then be moved relative to one another with a component of motion in a generally vertical direction so as to move the microelectronic element and the dielectric layer away from one another for deforming or bending the leads to a vertically-extensive disposition. The leads are preferably flexible. Restraining straps may be connected to the dielectric layer and the substrate for limiting movement of the dielectric layer and the substrate away from one another. The restraining straps are preferably thicker and shorter than the leads. The moving step may include the step of peeling the first ends of the flexible leads away from the dielectric layer. In certain preferred embodiments, an electrically conductive bonding material is applied to the bottom of the projections for facilitating formation of a bond and electrical connection between the contacts and the projections of the flexible leads. The conductive bonding material may be a solder, a diffusion bonding alloy, a eutectic bonding material or a conducive polymer, and may be provided with a thin layer of gold to inhibit oxidation.
During or after movement of the substrate and the dielectric layer away from one another, a first encapsulant, such as a compliant layer, may be provided between the dielectric layer and the substrate. The first encapsulant may be provided by introducing a curable liquid between the dielectric layer and the substrate and around the leads. After the curable liquid has been injected, the assembly is exposed to a curing process for curing the curable liquid so as to provide a compliant layer between the dielectric layer and the substrate. The compliant layer preferably allows the leads to flex and bend during use of the connection component of the present invention. The first encapsulant may be either rigid or compliant.
A second encapsulant, such as a curable liquid, is then disposed between the dielectric layer and the substrate and the leads. The second encapsulant may also be either rigid or compliant. The steps of encapsulating the leads with a first encapsulant and disposing the second encapsulant between the dielectric layer and the substrate may occur simultaneously. The first and second encapsulants may comprise a common material or may be a different material. The first and second encapsulants may include silicones, silicone elastomers, silicone gels, flexibilized epoxies and epoxies.
After the connection component of the present invention is connected to a chip or other microelectronic element by electrically connecting the first ends of the leads to such chip or microelectronic element, the second conductive terminals at the second ends of the leads can be electrically connected to the contacts on another microelectronic element, such as a printed circuit board or other substrate. The first and second ends of the leads are preferably movable with respect to one another. The movability of the leads and terminals connected thereto will provide compensation for phenomena such coefficient of thermal expansion differences.
In other preferred embodiments, a substrate, such as a metallic sheet including copper may be juxtaposed with the first ends of the leads. The metallic sheet may be engaged with the projections at the first ends of the leads after removal of the removable layer. Alternatively, the metallic sheet may be juxtaposed with the second surface of the removable layer and the projections at the first ends of the flexible leads may be electrically connected to or bonded to the metallic sheet. The metallic sheet may be juxtaposed with the removable layer before or after conductive metal is deposited over the removable layer. Preferably, the metallic sheet is electrically connected with the projections at the first ends of the flexible leads by fusing the projections with the metallic sheet.
After the removable layer is removed as set forth above, the metallic sheet and the dielectric layer may then be moved relative to one another with a component of motion in a substantially vertical direction so as to move the metallic sheet and the dielectric layer away from one another and to bend the flexible leads into a generally vertically extensive disposition. An encapsulant layer may be provided between the dielectric layer and a metallic sheet such as by introducing a curable liquid encapsulant between the dielectric layer and the metallic sheet and around the flexible leads. The encapsulant may be introduced during or after movement of the dielectric layer and the metallic sheet. The complaint layer may then be cured for providing a resilient layer between the dielectric layer and the metallic sheet and around the leads. Portions of the metallic sheet may then be removed to leave residual portions of the metallic sheet forming first conductive terminals electrically connected to the first ends of the leads. The portions of the metallic sheet may be removed either before or after the dielectric layer and the substrate are moved away from one another. This may be accomplished by depositing spots of an etch resistant substance, such as solder, over the bottom surface of the metallic sheet, as disclosed in commonly assigned U.S. patent application Ser. No. 08/989,312, the disclosure of which is incorporated herein by reference. The copper sheet may then be exposed to an etching solution for removing the portions of the copper sheet not covered by the solder mask.
Selectively etching away the copper sheet except for the portion of the sheet underlying the solder mask forms one or more conductive terminals electrically connected with the projections at the first ends of the leads. The terminals may then be electrically connected to the contacts of a first microelectronic element. The microelectronic element may include a circuit board, a wafer, a flexible circuit, a dielectric layer, a test socket, one or more packaged semiconductor chips, or one or more bare semiconductor chips. The first microelectronic element may then be moved away from the dielectric layer in a generally vertical direction so that the flexible leads are deformed to a vertically extensive disposition. A compliant layer may be formed between the dielectric layer and the first microelectronic element as described above.
In certain preferred embodiments the first microelectronic element may include a wafer having a plurality of semiconductor chips, whereby after the compliant layer has been formed between the wafer and the dielectric layer, the wafer is severed to provide individual units, each unit including one or more of the semiconductor chips with terminals and leads connected to the one or more chips.
In further preferred embodiments, methods of making the connection component may include the step of providing two or more removable layers and one or more dielectric layers for fabricating a multi-layer structure having two or more layers of flexible leads. The connection component of the present invention can also be connected to another connection component of the present invention.
As mentioned above, certain embodiments of the present invention may include restraining straps having one end connected to a dielectric layer and an opposite end connected to a substrate, such as a conductive metal sheet or microelectronic element. The restraining straps are generally shorter and thicker than the leads for limiting movement of the dielectric layer and the substrate/microelectronic element away from one another. The restraining straps may comprise the same material as the leads, such as copper, and may be formed simultaneously with the leads during the depositing a conductive metal step described above.
These and other objects, features and advantages of the present invention will be more readily apparent from the detailed description of the preferred embodiments set forth below, taken in conjunction with the accompanying drawings.